PHILLIPS, Calif. — Gov. Jerry Brown on Wednesday ordered mandatory water use reductions for the first time in California’s history, saying the state’s four-year drought had reached near-crisis proportions after a winter of record-low snowfalls.

Mr. Brown, in an executive order, directed the State Water Resources Control Board to impose a 25 percent reduction on the state’s 400 local water supply agencies, which serve 90 percent of California residents, over the coming year. The agencies will be responsible for coming up with restrictions to cut back on water use and for monitoring compliance. State officials said the order would impose varying degrees of cutbacks on water use across the board — affecting homeowners, farms and other businesses, as well as the maintenance of cemeteries and golf courses.

While the specifics of how this will be accomplished are being left to the water agencies, it is certain that Californians across the state will have to cut back on watering gardens and lawns — which soak up a vast amount of the water this state uses every day — as well as washing cars and even taking showers.

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“People should realize we are in a new era,” Mr. Brown said at a news conference here on Wednesday, standing on a patch of brown and green grass that would normally be thick with snow at this time of year. “The idea of your nice little green lawn getting watered every day, those days are past.”

Owners of large farms, who obtain their water from sources outside the local water agencies, will not fall under the 25 percent guideline. State officials noted that many farms had already seen a cutback in their water allocations because of the drought. In addition, the owners of large farms will be required, under the governor’s executive order, to offer detailed reports to state regulators about water use, ideally as a way to highlight incidents of water diversion or waste.

Because of this system, state officials said, they did not expect the executive order to result — at least in the immediate future — in an increase in farm or food prices.

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Weeds grow in what used to be the bottom of Lake McClure.Credit
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State officials said that they were prepared to enforce punitive measures, including fines, to ensure compliance, but that they were hopeful it would not be necessary to do so. That said, the state had trouble reaching the 20 percent reduction target that Mr. Brown set in January 2014 when he issued a voluntary reduction order as part of declaring a drought emergency. The state water board has the power to impose fines on local water suppliers that fail to meet the reduction targets set by the board over the coming weeks.

The governor announced what amounts to a dramatic new chapter in the state’s response to the drought while attending the annual April 1 measuring of the snowpack here in the Sierra Nevada. Snowpacks are critical to the state’s water system: They store water that falls during the wet season, and release it through the summer.

In a typical year, the measure in Phillips is around five or six feet, as Frank Gehrke, chief of the California Cooperative Snow Survey Program, indicated by displaying the measuring stick brought out annually. But on Wednesday, Mr. Brown was standing on an utterly dry field after he and Mr. Gehrke went through the motions of measuring a snowpack. State officials said they now expected the statewide snowpack measure to be about 6 percent of normal.

“We are standing on dry grass, and we should be standing on five feet of snow,” Mr. Brown said. “We are in an historic drought.”

Water has long been a precious resource in California, the subject of battles pitting farmer against city-dweller and northern communities against southern ones; books and movies have been made about its scarcity and plunder. Water is central to the state’s identity and economy, and a symbol of how wealth and ingenuity have tamed nature: There are golf courses in the deserts of Palm Springs, lush gardens and lawns in Los Angeles, and vast expanses of irrigated fields of farmland throughout the Central Valley.

Given that backdrop, any effort to force reductions in water use could be politically contentious, as Mr. Brown himself acknowledged. “This will be somewhat of a burden — it’s going to be very difficult,” he said. “People will say, ‘What about the farmers?’ Farmers will say, ‘What about the people who water their lawns?’ ”

Within hours of Mr. Brown’s announcement, Representative Kevin McCarthy, the California Republican who is the House majority leader, announced plans to renew efforts in Congress to pass legislation requiring the building of two huge water facilities in the state. The efforts had been blocked by Democrats concerned that the water projects would harm the environment and damage endangered species of fish.

“The current drought in California is devastating,” Mr. McCarthy said. “Today’s order from the governor should not only alarm Californians, but the entire nation should take notice that the most productive agriculture state in the country has entered uncharted territory.”

“I’m from the Central Valley, and we know that we cannot conserve or ration our way out of this drought,” he said.

The newly mandated 25 percent cut is in relation to total water use in the state in 2013. Cuts will vary from community to community, reflecting that per capita water use reduction has been better in some areas than others. In addition, the state and local governments will offer temporary rebate programs for homeowners who replace dishwashers and washing machines with water-efficient models.

Mr. Brown said the state would impose water-use restrictions on golf courses and cemeteries and require that nonpotable water be used on median dividers.

Lawns consume much of the water used every year in California, and the executive order calls for the state, working with local governments, to replace 50 million square feet of ornamental turf with planting that consumes less water.

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A hotel worker hosed a sidewalk in San Francisco last year. Such water use can now bring fines.Credit
Justin Sullivan/Getty Images

The order also instructs water authorities to raise rates on heavy water users. Those pricing systems, intended to reward conservers and punish wasters, are used in some parts of this state and have proved effective, state officials said.

Felicia Marcus, the chairwoman of the State Water Resources Control Board, said that California would leave it to local water providers to decide how to enforce the reductions on homeowners and businesses. She said she anticipated that most of the restrictions would be aimed at the outdoor use of water; many communities have already imposed water restrictions on lawns and gardens, but Ms. Marcus suggested they had not gone far enough.

“We are in a drought unlike one we’ve seen before, and we have to take actions that we haven’t taken before,” she said. “We are not getting the level of effort that the situation clearly warrants.”

Mark W. Cowin, the director of the California Department of Water Resources, said the state would tightly monitor compliance, in the hope that would be enough to accomplish the 25 percent reduction. If it is not, the order authorizes water suppliers to penalize offenders.

“We are looking for success, not to be punitive,” Mr. Cowin said. “In the end, if people and communities don’t comply, there will be repercussions, including fines.”

Correction: April 14, 2015

An article on April 2 about a decision in California to impose mandatory water restrictions for the first time misstated the amount of ornamental turf expected to be replaced with plantings that consume less water. It is 50 million square feet, not acres.

A version of this article appears in print on April 2, 2015, on Page A1 of the New York edition with the headline: California Puts Mandatory Curbs on Water Use. Order Reprints|Today's Paper|Subscribe